Frequency is a quality of AC signals which is measured for a variety of reasons. Companies involved with power generation and transmission need to know the fundamental frequency of the power, which in the United States should be 60 Hz. Frequency is not an instantaneous value. Thus, in order to determine frequency, information is required over some time period. A computed frequency value always represents the average frequency over some interval.
Generally, it is desirable to determine the fundamental frequency very quickly and accurately. Most frequency determination devices which are extremely accurate can take minutes to determine frequency. However, power producers and others involved in power distribution need virtually instantaneous frequency values (on the order of millisecond response times) in order to properly control the production and transmission of power having a known, stable fundamental frequency. The solution for such companies typically involves expensive equipment which has both the desired accuracy and response time. There thus exists the need for relatively inexpensive equipment which nonetheless accomplishes fast, accurate determination of the fundamental frequency of an AC signal having a known desired frequency.